An inverter is an electrical device enabling generation of a voltage with a variable frequency. One example of an inverter is a converter bridge implemented by IGB transistors (IGBT, Insulated-gate Bipolar Transistor) or other power semiconductors. Inverters have been used in connection with motors for controlling them with a variable frequency or, correspondingly, when electrical power is transmitted back to the network, whereby the inverter generates a voltage with a frequency that corresponds to the frequency of the network. Such an inverter feeding the network is referred to as a network inverter.
An inverter may also be a part of a frequency converter used for controlling a motor or another load, for example. Known frequency converters are formed of two converters, (e.g., a rectifier and an inverter) between which there is a direct-voltage or direct-current intermediate circuit. The rectifier and the inverter may also be positioned physically separated from each other and one rectifier may feed several inverters via a common intermediate circuit or, alternatively, several rectifiers may feed one inverter. An example of a rectifier is a diode bridge or a thyristor bridge.
Frequency converters can also include one or more choke devices. Examples of such choke devices used in or in connection with frequency converters include an input choke connected to the input of the rectifier of the frequency converter, and an output choke connected to the output of the inverter of the frequency converter.
Frequency converter structures presently in use include an input choke, an input bridge, a capacitor bank and an IGBT module. A structure-specific electrical circuit may also contain a brake power module (brake chopper) and an output choke (e.g. LC, LCL or LCR connection). Up to protection class IP20 (Ingress Protection), mechanical devices are constructed with one blower, in which the main flow of cooling medium, such as air, is conveyed to the cooling element of the power semiconductors and to other objects by the kind of distribution they use. The cooling element can, as a rule, be a one-part or a multi-part element, the parts being bunched together with support mechanics.
In protection class IP21 or in higher protection classes, the electronics space (what is called clean room) and the space for the cooling element (what is called dirty room) are separated from each other for practical reasons. In order for both spaces to have the right amount of air, both spaces can be provided with a blower of its own. The possible input choke can be positioned on the dirty side, either in a separate air space or in the space following the cooling element. Alternatively, the possible AC input choke may also be replaced by a DC choke connected to the intermediate circuit but in this case, too, the mechanical position of the choke is in the same place. The possible structure-specific output choke can be positioned mechanically in the same place as the input choke. In some structures, the possible chokes are positioned completely outside the device, in which case they can be, due to the cooling and their own support mechanism, larger in size than they would be if integrated.
Known inverter and frequency converter structures or motor controller structures can be problematic, for example, with regard to arranging the cooling. Although the size of the cooling element or elements has continuously been on the decrease owing to more accurate designing, smaller losses and physically smaller power semiconductors, the amount of air (or amount of another cooling medium) relative to the outer dimensions of the device has even increased. Also, distribution of a sufficient amount of air can be, for example, performed using a large blower at a low blasting rate, taking into account the power, sound and service life of the blower. For this reason, the space used by the cooling is, relative to the size of the device, rather large in known solutions. This is further emphasized in, for example, IP21 or higher protection classes.